Although it is often proposed that the non-coding DNA at the 5' end of structural genes in eukaryotes contain various kinds of regulatory information, the nature of the regulatory elements and their mode of action is not all clear. In Drosophila, mutants which affect the tissue distribution of a few enzymes have been recovered. More commonly, mutants are found which affect the level of a given gene product in all tissues. In no case has it been possible to determine the location of the regulatory mutant in the DNA or the level at which such mutants exert their effect on the control of gene expression. We have identified two closely linked cis-acting regulatory mutants which lead to an increased expression of two related and adjacent genes, dopa decarboxylase (Ddc) and the alpha methyl dopa hypersensitive gene 1(2)amd. Our first goal is to combine fine structure mapping and molecular analysis using cloned DNA to locate the regulatory mutations at the DNA level. Our second goal is to determine the mechanism which regulates the level of gene product. For this we will determine gene copy number to test for possible somatic gene amplification and then measure RNA levels to determine if altered transcription or RNA accumulation is responsible. If no differences in nuclear or cytoplasmic RNA are found we will determine rates of synthesis and degradation of the enzyme. Our goal is to test the notion that a higher order organization exists in which the unit of regulation is a domain of several genes. We will examine the chromatin structure in the Ddc region directly using DNAse I sensitivity as a measure of state of activation. We will also examine the genes surrounding Ddc and amd for functional relationships by determining their program of developmental expression and their effect on cuticle maturation.